Previous literature on learners' epistemological beliefs about physics has almost exclusively focused on analysis of university classroom instruction and its effects on students' views. However, little is known about other populations or factors other than classroom instruction on learners' epistemologies. In this study, we used a cross-sequential method, combining both longitudinal and cross-sectional designs, to investigate an epistemological progression trend from preservice to in-service teachers. Six cohorts of participants were studied, who either were then attending or had completed an undergraduate teacher preparation program in physics at a major Chinese university. These cohorts were incoming freshmen, end-of-year freshmen, end-of-year sophomores, end-of-year juniors, end-of-year seniors, and 1st-year high school physics teachers who were about to enter the 2nd year of teaching. We used the Colorado Learning Attitudes about Science Survey (CLASS) as both a pretest and a post-test to gauge the changes in the participants' epistemological views over an entire academic year. Follow-up interviews were also conducted to explore factors responsible for such changes. Results showed that the epistemological trend as measured by CLASS did not increase monotonically. Instead, there was a decrease in the epistemological trend among the incoming freshmen in their first year undergraduate studies, followed by a long stasis until the end of the senior year. Then, there was a rebound for the end-of-year seniors in their 1st year of teaching, followed by another plateau. Interviews revealed that the competitive learning environment, increased content difficulty, and unfamiliar pedagogies in college were major factors that negatively influenced incoming freshmen's views about physics. Conversely, a role change from student to teacher and relatively easy content in high school positively impacted end-of-year seniors' views about physics and learning.